Electric circuit interrupter



Jan. 30, 1940.

H. BURMEISTER ELECTRIC CIRCUIT INTERRUPTER Filed March 25, 1937 w CELLULOS/C MATERIAL YIELD/1V6 AN UX/D/Z/NG 6 45 0R MIXTURES THEREDF, fl/VD All INPRE'GNANT F0 S/l/D MASS CO/TFR/S/NG' SYN ThET/C RES/N OF THE UREA TYPE,

Inventor: HeT-Ynann Burmeiste'r,

flaw a7 His Attorney.

Patented Jan. 30, 1940 PATENT OFFICE ELECTRIC CIRCUIT INTERRUPTER Hermann Burmeister, Berlin-Spandau,

Ger-

many, assignor to General Electric Company, a corporation of New York Application March 23, 1937, Serial No. 132,661

In Germany March 31, 1936 8 Claims, This invention relates to electric circuit interrupters, and more particularly to circuit inter-,

rupters of the air-break expulsion type wherein a gas formed by decomposition of a material by the are upon opening of the circuit is utilized to interrupt the arc. The invention is especially concerned with insulating or arc-extinguishing tubes in which such arcs are formed during service use of the tube.

It is known to use as materials for the arcextinguishing or quenching tubes of electric gas switches, from the walls of which at the switching-ofi of the current the quenching gas is liberated by the resulting-arc, inorganic substances,

5 especially substances capable of yielding water under the are heat, for example boric acid or the like. Such substances have the objectionable feature that they are diificult to form into the desired shape- It also is known to make use of organic substances, for instance fibre, in the construction of arc-interrupting tubes. However, materials of this nature often do not adequately retain their shape during service use. Furthermore, it also has been proposed to employ pressed insulating substances composed of a fibrous material and a cementing agent, more particularly an artificial resin which, in hardened state, is capable of evolving an arc-interrupting gas under the heat of the arc. In arc-interrupting tubes of this construction the fibrous material adds strength to the structure. When using such pressed insulating compositions there is, however, experienced in every case the difliculty that after a large current has been switched off, the coveringof the individual fibres is converted into gas,

and thus is lost. The framework-forming material remaining at the surface can serve only imperfectly even for the switching-oi! of comparatively weak currents.

In order to obviate the drawbacks from which the known framework-forming materials suffer it has also been proposed to employ as material for the quenching tubes a fibrous material able to be transformed into a horny state, the horny material then being subjected to an after-treatment in a. solution of urea, polyhydric alcoholpolybasic acid resin or a similar artificial resin, and finally to a drying-process.

The present invention starts from this lastmentioned proposal. In practicing the invention I may use hydrated cellulose not only in the form of fibre but also in any other form as the substance constituting the framework of the arcinterrupting' structure. Or, I may use for this purpose cellulosic substances of another kind containing oxidizing agents, say nitrated cellulose. The framework-forming substance is molded in loosened or incompact state together with urea resin or with the individual components thereof one after the other, after which 6 the composition is molded into tubular shape and hardened.

My invention will be set forth more fully in the following description referring to the accompanying drawing, and the features of novelty 10 which characterize my invention will be pointed out with particularity in the claims annexed to andforming a part of this specification.

Referring to the drawing the single figure thereof is an elevational View, partly in section, 15 of an electric circuit breaker of the expulsion type to which the present invention is applicable.

There is shown merely by way of example an electric circuit interrupter, more particularly a circuit breaker having means such as the sta- 20 tionary contact I and the movable rod contact 2, for opening the circuit so as to form an arc, and an insulating structure 3 forming an arc chamber for closely confining the are between the contacts. The insulating structure 3 consists of a 2 5 tubular member closed at the fixed contact end open at the other end for receiving the rod contact. Upon opening of the circuit, separation of the contacts I and 2 causes formation of an are which decomposes some of the material of the are 30 chamber walls 3. The gas so formed is under considerable pressure by reason of the comparatively close fit of the rod contact 2 and the tube 3, with the result that when the rod leaves the tube a blast of gas is released as indicated for 35 interrupting the are.

In accordance with the present invention the insulating structure 3 comprises an incompact mass of cellulosic substance selected from the class consisting of hydrated cellulose, cellulosic 40 material yielding an oxidizing gas, and mixtures of hydrated cellulose and cellulosic material yielding an oxidizing gas, and an impregnant for the said mass comprising hardened synthetic resin of the urea type filling the mass to form a 45 mechanically strong structure. In this structure both thechosen cellulosic'substance and the impregnant' are capable of delivering arc-extinguishing gas under the heat of the are.

The method according to this invention ren- 50 clers possible a. very intimate penetration and strong enveloping or covering of the loosened framework-forming substance with the gas-gem. crating cementing medium. Such results cannot beobtained if, for instance, a hydrated cel- 55 lulose converted into a horny state, as for instance whitehom fibre, is intermixed with urea resins. Quenching tubes manufactured according to this invention are characterized by great mechanical solidity and excellent gas-delivering properties both of the framework-forming material and of the cementing medium or impregnant, together with water-repelling properties such that the tube satisfactorily will maintain its shape during service use. Further, this construction eliminates the possibility of. a deposition of soot on the walls of the switch-chamber.

Hydrated cellulose is particularly distingushed by the property that when used as framework for the quenching tube it supplies gas in the heat of the arc with a particularly small formation of carbon. If a cellulosic material of another kind be used instead of it, or in conjunction therewith, provision must be made that such cellulosic material contain an oxidizing agent. As an example I mention nitrated cellulose, but instead thereof celluloses pro-treated with an inorganic nitrate solution, for instance a solution of ammonium nitrate, may be used.

In carrying the present invention into effect the loosened or incompact mass of hydrated cellulose may be impregnated while it is in the form of either a continuous sheet or an aqueous pulp. Depending upon the condition or state of the material at the beginning of the treatment, the ultimate shaping or molding in the form of quenching tubes is effected either with the aid of winding machines or of molds.

It is likewise possible to proceed in such a way that the starting material comprising loosened hydrated cellulose is, prior to being shaped or molded, supplied with, the individual components of the urea resin, or with the condensate in its initial state. When the material is being transformed into quenching tubes, the condensation of the urea resin then takes place upon the framework-forming substance.

It is also advantageous to employ as starting material a porous sponge-like hydrated cellulose such as can be obtained, for instance, by means of the viscose process. This starting material is impregnated in the above-described 'manner either with the urea resin itself or with its individual components and is then shaped or molded while the resin is being converted to a hardened state.

It has also been found to be advantageous to dry a loosened hydrated cellulose down to about 10% of water and then, shortly before the conversion into horn commences, to impregnate it with urea resin itself or with its individual components, whereupon the ultimate molding takes place. I

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric circuit interrupter, an arcextinguishing tube. comprising an incompact mass of cellulosic substance selected from the class consisting of hydrated cellulose, cellulosic material yielding an oxidizing gas, and mixtures of hydrated cellulose and cellulosic material yielding an oxidizing gas, and an impregnant for the said mass comprising hardened synthetic resin of the urea type filling the mass to form a mechanically strong structure wherein, under the heat of an arc, both the said cellulosic substance and the said impregnant are capable of delivering arc-extinguishing gas.

2. In an electric circuit interrupter, an arcextinguishing tube comprising an incompact mass of hydrated cellulosic material and an impregnant comprising hardened synthetic resin of the urea type filling said. mass to'form a mechanically strong structure wherein, under the heat of an arc, both the said hydrated cellulosic material and the said impregnant are capable of delivering arc-extinguishing gas. a

3. In an electric circuit interrupter, an arcextinguishing tube formed of an incompact mass com-prising cellulosic material yielding an oxidizing gas, and an impregnant of hardened synthetic resin of the urea type filling said mass to form a. mechanically strong structure wherein, under the heat of an arc, both the said cellulosic material and the said impregnant are capable of delivering arc-extinguishing gas.

'4. In an electric circuit interrupter, an arcextinguishing tube formed of an incompact mass comprising cellulosic material containing. a nitrate radical and an impregnant of hardened synthetic resin of the urea type filling said mass to form a mechanically strong structure wherein, under the heat of an arc, both the said cellulosic material and the said impregnant are capable of delivering arc-extinguishing gas.

5.'In an electric circuit interrupter, an arcextinguishing tube formed of a substance comprising an incompact mass of hydrated cellulose as one component and cellulose nitrate as another component, and an impregnant of hardened synthetic resin of the urea type filling said mass to form a mechanically. strong structure wherein, under the heat'of an are, both the components of the said mass and the said impregnant are capable of delivering arc-extinguishing gas.

6. In an electric circuit interrupter, an arc- -extinguishing tube formed of a substance comprising an incompact mass of hydrated cellulose as one component and cellulosic material pre-treated with an inorganic nitrate solution as another component, and an impregnant for the said mass comprising hardened synthetic resin of the urea type filling the mass to form a mechanically strong structure wherein, under the heat of the are, both the components of the said mass and the said impregnant are capable of delivering arc-extinguishing gas.

'7. In an electric circuit interrupter, an arcextingulshing tube formed of an incompact mass comprising cellulosic material pre-treated with an inorganic nitrate solution, and an impregnant for the said mass comprising hardened synthetic resin of the urea type filling the mass to form a mechanically strong structure wherein, under the heat of the arc, both the said cellulosic material and the said impregnant are capable of delivering arc-extinguishing gas.

8. In an electric circuit interrupter, an arc- I extinguishing tube as in claim '7 wherein the inorganic nitrate solution is a solution of ammonium nitrate.

HERMANN BURMEISTER. 

